This application is based on Japanese Patent Application No. 2002-266948 filed on Sep. 12, 2002, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vapor-compression refrigerant cycle with a control unit for determining a lock of a compressor. The vapor-compression refrigerant cycle is suitably used for a vehicle air conditioner.
2. Related Art
In a control unit of a vapor-compression refrigerant cycle described in U.S. Pat. No. 5,197,298 (corresponding to JP-B2-820151), a lock (fixing) of a sliding portion of a compressor is determined based on a pressure of high-pressure refrigerant. However, the pressure of the high-pressure refrigerant in the refrigerant cycle changes in accordance with a change of a thermal load (i.e., air-conditioning load) of the refrigerant cycle. Therefore, it is difficult to accurately determine whether or not the compressor is locked up, and lock phenomenon (fixing phenomenon) may be incorrectly detected.
In view of the above-described problems, it is an object of the present invention to provide a vapor-compression refrigerant cycle with a control unit for accurately determining a lock of a compressor.
It is another object of the present invention to provide a lock detection device of the compressor, which prevents a lock from being incorrectly detected.
According to the present invention, a vapor-compression refrigerant cycle includes a compressor for compressing refrigerant, a high-pressure heat exchanger for cooling high-pressure refrigerant discharged from the compressor, a decompression unit for decompressing refrigerant from the high-pressure heat exchanger, a low-pressure heat exchanger for evaporating low-pressure refrigerant after being decompressed in the decompression unit by performing heat exchange between the low-pressure refrigerant and air passing through the low-pressure heat exchanger, a first air temperature detector for detecting an air temperature before being heat-exchanged in the low-pressure heat exchanger, and a second air temperature detector for detecting an air temperature after being heat-exchanged in the low-pressure heat exchanger, and a control unit for controlling a displacement of the compressor. Further, the control unit has a lock determining means for determining a lock of a sliding portion of the compressor. In the control unit of the vapor-compression refrigerant cycle, the lock determining means determines that the sliding portion of the compressor is locked, at least when a control signal where the displacement of the compressor is equal to or larger than a predetermined value is output from the control unit, and when an absolute value of a temperature difference between the air temperature before being heat-exchanged in the low-pressure heat exchanger and the air temperature after being heat-exchanged in the low-pressure heat exchanged is equal to or smaller than a predetermined temperature. Therefore, the lock of the sliding portion of the compressor can be accurately detected.
Preferably, the lock determining means determines that the sliding portion of the compressor is locked, when the control signal where the displacement of the compressor is equal to or larger than the predetermined value is output from the control unit, and when the absolute value of the temperature difference is equal to or smaller than the predetermined temperature, and further when a pressure of the high-pressure refrigerant detected by a refrigerant pressure detector tends to be reduced. In this case, the lock of the compressor can be more accurately detected.
More preferably, the lock determining means determines that the sliding portion of the compressor is locked, when the control signal where the displacement of the compressor is equal to or larger than the predetermined value is output from the control unit, when the absolute value of the temperature difference is equal to or smaller than the predetermined temperature, and when the pressure of the high-pressure refrigerant detected by the refrigerant pressure detector tends to be reduced, and further when the air temperature detected by the second air temperature detector tends to be increased. Further, the lock determining means determines that the sliding portion of the compressor is locked, when the control signal where the displacement of the compressor is equal to or larger than the predetermined value is output from the control unit, when the absolute value of the temperature difference is equal to or smaller than the predetermined temperature, when the pressure of the high-pressure refrigerant detected by the refrigerant pressure detector tends to be reduced, and when the air temperature detected by the second air temperature detector tends to be increased, and further when an absolute value of a temperature difference between a target temperature of air after being heat-exchanged in the low-pressure heat exchanger and the air temperature detected by the second air temperature detector is larger than a set value. In this case, it can prevent the lock of the compressor from being incorrectly detected.